1. Field of the Invention
The present invention relates to a method of manufacturing a recording medium and the recording medium for use in a magnetic recording and reproduction device such as a hard disk drives serving as a secondary storage device of computers.
2. Description of the Related Art
In recent years, there has been an increasing need for high-density recording in magnetic storage devices such as hard disk drives. In such hard disk drives for high-density recording, it is necessary to reduce the magnetic spacing, which is a space formed between a magnetic head provided in the magnetic disk drives and the surface of a magnetic disk serving as a recording medium in the main body of the hard disk drives, as much as possible. In other words, the gap between the magnetic head and the magnetic disk surface, scanned by the magnetic head, should be as small as possible.
FIG. 1 is a schematic diagram showing a magnetic disk drive 100 including a magnetic head 120 and a rotatable magnetic disk 110 of the related art. FIG. 1 is illustrated in an enlarged view; so as to clearly show the layered structure of the magnetic disk 110 and magnetic spring S.
Referring to FIG. 1, the magnetic disk has a multilayered structure including a substrate 111, an underlayer 113 formed on the substrate 111, and a magnetic layer 115 formed on the underlayer 113. A protection layer 117 of amorphous carbon is provided on the magnetic layer 115.
The magnetic disk drive 100 described above generally operates in accordance with the so-called contact-start-stop (CSS) mode. With the CSS mode, a lift surface 120a of the magnetic head 120 contacts and slides over the surface of the magnetic disk 110 at the start or stop phase of rotation of the magnetic disk 110. The magnetic disk 110 has a CSS area within its surface. The magnetic head 120 contacts the CSS area when the magnetic disk 110 starts and stops rotating. On the other hand, the magnetic head 120 can float in the air with airflow caused by the rotation of the magnetic disk 110 when the magnetic disk drive 100 operates.
However, even during steady state operation, the magnetic head 120 may come into contact with the surface of the magnetic disk 110 due to unexpected affairs. To accommodate the continuous contact between the head 120 and the disk 110 when the drive starts or stops and the intermittent contact between the head 120 and the disk 110 when the head collides with unexpected affairs, the surface of the magnetic disk 110 should have both a low coefficient of friction and a high resistance to abrasion.
The magnetic disk 110 has a lubrication layer 119, which is formed by lubricant, on the protection layer 117. As the lubricant layer 119 has influence on the friction and the abrasion properties of the magnetic disk 110, it is important to keep the lubrication layer 119 in good conditions for maintaining the reliability of the magnetic disk drive 100.
In the near future, still lower spacing between the magnetic head 120 and the surface of the magnetic disk 110 will be required for high-density recording. Thus, it is really important to keep the surface of the magnetic disk 110 with a low coefficient of friction, a high resistance to abrasion and water repellency over a longer period of time.
However, the inside of the magnetic disk drive 100 reaches a high temperature. Furthermore, the magnetic disk 110 rotates at high speed in the drive 100. Even under the most benign ambient conditions, the interior of the disk drive 100 is a high-temperature environment due to the high rate of rotation of the disk 110 relative to the head 120. Increasing the rate of rotation of the disk 110 increases the centrifugal force that acts on any element of the lubrication layer 119; increasing the temperature of the disk 110 also increases the mobility of the elements of the lubrication layer 119. Elements of the lubrication layer 119 thus tend to move towards the circumference of the disk 110 over time, where they are more likely to be spun off the disk 110, so that the lubrication layer 119 tends to become thinner as the service time of the disk increases. A thinning lubrication layer 119 loses the capability of fulfilling its several roles. In order to prevent the lubrication layer 119 from losing the capability, the lubrication layer 119 should be formed by lubricant having strong adsorptive property to the surface (the protection layer 117) of the magnetic disk 110.
Concerning the lubrication layer 119 on the protection layer 117, it is considered that the lubrication layer 119 consists of a “bonding sub-layer” 119a, which consists of molecules that bind strongly to the protection layer 117, and a “mobile sub-layer” 119b, which consists of molecules that bind weakly to the protection layer 117. The mobile sub-layer 119b tends to undergo spin off as a result of centrifugal force by the disk rotation. It is estimated as a main reason of the thinning of the lubrication layer 119 as described above that the mobile layer 119b tends to move to the circumferential part of the magnetic disk 110 and much mobile sub-layer 119b breaks away from the magnetic disk 110 in the end.
It is important to maintain the original thickness of the lubrication layer 119 as much as possible, even for the magnetic disk 110 that is used for a long period of time. Thinning of the lubrication layer 119 is associated with loss of the mobile sub-layer 119b. Minimizing the thinning of the lubrication layer is accomplished by maximizing the “bonding ratio” of the lubrication layer, which is the ratio of the bonding sub-layer 119a to the mobile sub-layer 119b. 
Many prior arts disks attempted to increase the thickness of the bonding sub-layer 119a. In the prior arts, a lubricant is applied to the protection layer 117 of the magnetic disk 110, and ultraviolet rays curing treatment or heating treatment is implemented on the lubrication layer 119 (lubricant) for increasing the ratio of the bonding sub-layer 119a (the bonding ratio).
However, it is not enough for increasing the bonding ratio to implement the above treatment only one time.